To use this solution with a version of sed that does not accept newlines in patterns (i.e. to make it portable), one has to put the commands in a sed commands file and run it with sed -f.

How to make the one-liner portable without using a sed commands file?

Maybe something like:

  sed 's/baz/elephant/;/^ \{2\}- elephant/{h;G;};/^ \{4\}- elephant/{h;G;};s/elephant/baz/' foo|sed -a wfoo

  1. s/baz/elephant/ 
  2. duplicate that line if two or four space indent
  3. s/elephant/baz/
  4. save

N.B. no temp file used to save changes

cf. jvns.ca blog:

  1. search for baz
  2. copy that line and paste it
  3. s/baz/elephant/
  4. save and quit

N.B. temp file in $TMPDIR used to save changes